Host controlled enablement of automatic background operations in a memory device

ABSTRACT

A host that is coupled to a memory device is configured to read a status register of the memory device to determine if the memory device supports host controlled enablement of automatic background operations. The memory device responds to the host regarding whether the memory device supports host controlled enablement of automatic background operations. The host can enable the automatic background operations if the memory device supports this feature. The host can then set a time period in the memory device that is indicative of when the memory device can automatically perform the background operations.

TECHNICAL FIELD

The present embodiments relate generally to memory and a particularembodiment relates to host controlled enablement of automatic backgroundoperations in a memory device.

BACKGROUND

Memory devices are typically provided as internal, semiconductor,integrated circuits in computers or other electronic devices. There aremany different types of memory including random-access memory (RAM),read only memory (ROM), dynamic random access memory (DRAM), synchronousdynamic random access memory (SDRAM), and non-volatile (e.g., flash)memory.

Flash memory devices have developed into a popular source ofnon-volatile memory for a wide range of electronic applications. Flashmemory devices typically use a one-transistor memory cell that allowsfor high memory densities, high reliability, and low power consumption.Changes in threshold voltage of the cells, through programming of acharge storage structure, such as floating gates, trapping layers orother physical phenomena, determine the data state of each cell. Commonuses for flash memory include personal computers, personal digitalassistants (PDAs), digital cameras, digital media players, digitalrecorders, games, appliances, vehicles, wireless devices, cellulartelephones, and removable memory modules.

In addition to performing access operations such as read and write, anon-volatile memory device also performs background operations. Forexample, the memory device might perform a wear leveling operation bymoving data around within the memory array of the memory device. Anotherbackground operation might be a housekeeping operation that removesobsolete data in order to free up memory blocks to be erased and reused.These operations are performed in the background typically without theknowledge of the host and, in some embodiments, are performedautomatically by the memory device (e.g., are initiated without beingcommanded by the host).

A problem can occur when these background operations are being performedby the memory device without the knowledge of the host. The host caninterrupt the background operation by sending an access command orturning off the power to the memory device. This can result in lost orcorrupted data and might require the memory device to start thebackground operation over, thus resulting in a loss of performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of one embodiment of a portion of aNAND architecture memory array.

FIG. 2 shows a block diagram of one embodiment of a system that canincorporate a non-volatile memory device using a method for hostcontrolled enablement of automatic background operations.

FIGS. 3A and 3B show flowcharts of embodiments of the method for hostcontrolled enablement of automatic background operations.

FIG. 4 shows a diagram of a check and configuration phase of the methodfor host controlled enablement of automatic background operations.

FIG. 5 shows a diagram of an execution phase of the method for hostcontrolled enablement of automatic background operations.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof and in which is shown, byway of illustration, specific embodiments. In the drawings, likenumerals describe substantially similar components throughout theseveral views. Other embodiments may be utilized and structural,logical, and electrical changes may be made without departing from thescope of the present disclosure. The following detailed description is,therefore, not to be taken in a limiting sense.

Non-volatile memory can utilize different architectures including NORand NAND. The architecture designation is derived from the logic used toread the devices. In NOR architecture, a logical column of memory cellsis coupled in parallel with each memory cell coupled to a data line,such as those typically referred to as bit lines. In NAND architecture,a column of memory cells is coupled in series with only the first memorycell of the column coupled to a bit line.

FIG. 1 illustrates a schematic diagram of one embodiment of a portion ofa NAND architecture memory array 101 comprising series strings ofnon-volatile memory cells. This figure is for purposes of illustrationof a typical memory array only as a method for host controlledenablement of automatic background operations in a memory device and isnot limited to the illustrated NAND architecture.

The memory array 101 comprises an array of non-volatile memory cells(e.g., floating gate) arranged in columns such as series strings 104,105. Each of the cells is coupled drain to source in each series string104, 105. An access line (e.g., word line) WL0-WL31 that spans acrossmultiple series strings 104, 105 is coupled to the control gates of eachmemory cell in a row in order to bias the control gates of the memorycells in the row. Data lines, such as even/odd bit lines BL_E, BL_O, arecoupled to the series strings and eventually coupled to sense circuitryand page buffers that detect and store the state of each cell by sensingcurrent or voltage on a selected bit line.

Each series string 104, 105 of memory cells is coupled to a source line106 by a source select gate 116, 117 (e.g., transistor) and to anindividual bit line BL_E, BL_O by a drain select gate 112, 113 (e.g.,transistor). The source select gates 116, 117 are controlled by a sourceselect gate control line SG(S) 118 coupled to their control gates. Thedrain select gates 112, 113 are controlled by a drain select gatecontrol line SG(D) 114.

In a typical prior art programming of the memory array, each memory cellis individually programmed as either a single level cell (SLC) or amultiple level cell (MLC). A cell's threshold voltage (V_(t)) can beused as an indication of the data stored in the cell.

For example, in an SLC memory device, a V_(t) of 2.5V might indicate aprogrammed cell while a V_(t) of −0.5V might indicate an erased cell. Inan MLC memory device, multiple V_(t) ranges can each indicate adifferent state by assigning a bit pattern to a specific V_(t) range.

FIG. 2 illustrates a functional block diagram of a memory device 200that can include a memory array architecture such as illustrated inFIG. 1. The memory device 200 is coupled to an external host 210 thatacts as some type of controller. The host 210 can be configured tocommunicate commands (e.g., write, read), control signals, and data withthe memory device 200 over a command and data bus 262 that connects thehost 210 with the memory device 200. The memory device 200 and the host210 form part of a system 220.

The memory device 200 includes one or more arrays 230 of memory cells(e.g., NAND architecture non-volatile memory cells). The memory array230 is arranged in banks of word line rows and bit line columns. In oneembodiment, the columns of the memory array 230 comprise series stringsof memory cells. One example of a portion of such an array isillustrated in FIG. 1.

Host interface circuitry 260 provides an interface between the memorydevice 200 and the host 210. The host interface circuitry 260 mightinclude circuitry such as buffers and registers.

Control circuitry 270, coupled to the host interface 260, operates inresponse to control signals from the host 210. These signals are used tocontrol the operations of the memory array(s) 230, including data sense(e.g., read), data write (e.g., program), and erase operations. Thecontrol circuitry 270 may be a state machine, a sequencer, or some othertype of control circuitry that is configured to control generation ofmemory control signals. In one embodiment, the control circuitry 270 isconfigured to control execution of the method for host controlledenablement of background operations.

Memory interface circuitry 275, coupled between the control circuitry270 and the memory array(s) 230, provides bidirectional datacommunication between the control circuitry 270 and the memory array(s)230. The memory interface circuitry 275 can include write circuitry,read circuitry, decoders, and buffers.

Memory device registers 290, coupled to the host interface 260 and thecontrol circuitry 270, can be a part of the control circuitry 270 orseparate from the control circuitry 270. The registers 290, assubsequently described, can be used to store control data for operationof the method for host controlled enablement of background operations.In one embodiment, the control circuitry 270 controls writing to andreading from the memory device registers 290 as directed by controlsignals from the host 210 over the command and data bus 262, assubsequently described. In another embodiment, the host 210 can writedirectly to and read directly from the registers 290 without controlcircuitry 270 intervention.

In one embodiment, the host interface 260, the control circuitry 270,the memory interface 275, and the memory device registers 290 are partof the memory device controller 201. Alternate embodiments of thecontroller 201 can include only a subset of these blocks or additionalmemory device circuitry.

The host can use the registers in the memory device to determine thestatus and capabilities of the memory device (e.g., status register),enable/disable automatic background operations of the memory device(e.g., enablement register), and/or set a minimum time period before thememory device can automatically perform (e.g., execute) or enablesautomatic background operations (e.g., time register). The registers caninclude different registers or different register bits in one registerfor enabling different background operations (e.g., allowing forselective enablement of different automatic background operations). Theautomatic background operations of the memory device can be anybackground operations performed in the memory device that do not requirehost initiation. For example, these background operations can includewear leveling, collection of bad or old data, unused memory blockerasing, and/or other memory housekeeping operations.

In operation, the memory device register can be set to a first state(e.g., logical 0) to indicate that the memory device does not supporthost controlled enablement of automatic background operations and asecond state (e.g., logical 1) to indicate that the memory devicesupports host controlled enablement of automatic background operations.If the host reads the state that indicates that the memory device doesnot support enablement of automatic background operations, this canindicate that the subsequently described registers (e.g., enablement,time) are not activated or not present. If the host reads the state thatindicates that the memory device supports enablement of automaticbackground operations, this can indicate that the subsequently describedregisters are also activated and/or present.

In one embodiment, the memory device register is a read only registerthat is programmed prior to being used. For example, when the memorydevice is manufactured, the memory device register of a particularmemory device can be programmed as supporting enablement of automaticbackground operations. In an alternate embodiment, the status registercan be programmed at a time after manufacture depending on theapplication of the system.

If the host determines that the memory device supports enablement ofautomatic background operations, the host can write control data to aparticular memory device register (e.g., enablement register) toenable/disable automatic background operations of the memory device. Forexample, the host can write a first state (e.g., logical 0) to theenablement register to indicate to the memory device that the memorydevice is allowed to initiate automatic background operations. In suchan embodiment, the memory device can automatically perform thebackground operations during any host idle time and/or during executionof read/write operations and/or other operations initiated by the host.

The host can write a second state (e.g., logical 1) to the enablementregister to indicate to the memory device that the host willperiodically enable the background operations. This indicates to thememory device not to automatically perform the background operations. Insuch a configuration, only the host will initiate the backgroundoperations.

In one embodiment, the enablement register is a write/read register.This allows the host to not only write to the register but also to readit later to determine if it has been reset or written to by the memorydevice controller.

The host can also write to particular control registers (e.g., timeregisters) in order to set a particular time period that indicates tothe memory device (e.g., controller) the minimum time period to waitafter completing the operation commanded by the last received hostcommand before automatically performing (e.g., initiating and/orexecuting) or enabling automatic background operations. The memorydevice can also decide not to take into account such time period set bythe host and start its background activity before new arriving hostcommands are executed without any impact on performance. The timeregisters can be write/read registers so that, for example, the host canload one time register with an actual time period value that the memorydevice should wait after completing the operation commanded by the lastreceived host command before automatically performing or enablingautomatic background operations. A second time register can be loadedwith the actual time period value's unit of measure (e.g., μs, ms, s).The memory controller can then use both time registers in combination todetermine how long to wait before automatically performing or enablingautomatic background operations. In an alternate embodiment, only onetime period register is used and it is assumed to have a fixed unit ofmeasure (e.g., μs, ms, or s).

In another alternate embodiment, the memory device might not have a timeregister. In such an embodiment, the memory device could have anotherparticular register (e.g., start register). If host enablement ofautomatic background operations is supported by the memory device, thehost can write control data (e.g., start data) to the start registerwhenever it is desired to start (e.g., initiate) background operations.This data can be automatically cleared by the memory controller afterthe background operations have begun to execute.

In yet another alternate embodiment, the memory device might have boththe time register(s) and the start register. In such an embodiment,instead of waiting for the time period in the time register aftercompleting the last operation commanded by the host before automaticallyperforming the background operations, the memory device would wait forthe time period in the time register after receiving the start data fromthe host before automatically performing the background operations.

In another alternate embodiment, the memory device can perform theautomatic background operations in response to an explicit command fromthe host while also having the capability of automatically performingthe automatic background operations without an explicit command from thehost. In yet another embodiment, the time register(s) could be used todetermine when to enable the automatic background operations instead ofwhen to begin performing the automatic background operations.

FIGS. 3A and 3B illustrate flowcharts of embodiments of the method forhost enablement of automatic background operations in a memory device.FIG. 3A illustrates a flowchart of a method that is executed by thehost. FIG. 3B illustrates a flowchart of a method that is executed bythe memory device.

As illustrated in FIG. 3A, the host first determines if the memorydevice supports the host controlled enablement of automatic backgroundoperations 301. As previously described, this can be accomplished byreading a register of the memory device. If the memory device supportshost controlled enablement of automatic background operations, the hostcan then enable the automatic background operations 303. This can beaccomplished by writing control data to another register of the memorydevice. If the memory device has one or more control registers for timeperiod values, the host can transmits the time period value to thememory device 305 along with, in one embodiment, the unit of measurevalue for the time period value. In another embodiment, the host cantransmit a start command 305 to the memory device when the host is donesending other commands and wishes the memory device to begin startbackground operations.

As illustrated in FIG. 3B, the memory device receives commands from thehost 310. The memory device then determines if any more commands havebeen received or if the memory device is experiencing an idle time 311during which no commands are received from the host. If another commandis received 310, the memory device executes the commands and againchecks for idle time 311. If the memory device is experiencing idle time311, it waits for the time period stored in the time register(s) toexpire 313 prior to automatically performing the background operations315.

In another embodiment, the memory device would be able to execute anautomatic background operation at the same time as receiving hostread/write commands. This could be accomplished without affecting theperformance of the read/write operations. Such a memory device would nottake into account any minimum idle time after completing the hostcommands but could initiate the automatic background operations evenbefore the read/write are completed.

If the memory device does not support the time period value register(e.g., it is not present or is not activated), the memory device candetermine if the last received command was a start command 313.Receiving this command indicates to the memory device to start thebackground operations.

FIGS. 4 and 5 illustrate examples of operation of the interactionbetween the host 400 and the memory device 401 as part of the method forhost enablement of automatic background operations in the memory device.These diagrams are for purposes of illustration only as the interactionbetween the host and the memory device can occur differently.

FIG. 4 illustrates a check and configuration phase of operation betweenthe host 400 and the memory device 401. The host 400 reads the statusregister 410 of the memory device 401 to determine if the memory device401 supports host controlled enablement of automatic backgroundoperations. If the memory device 401 supports this feature, the memorydevice responds 411 with the register data indicating that this featureis supported.

If the feature is supported, the host 400 can then write control data tothe enablement register 420 to configure this feature. The memory device401 can then acknowledge 421 that the feature has been activated.

Once the automatic background operations have been enabled, the host 400can transmit a time period value 430 to the memory device 401 to bestored in the time register. As previously discussed, this can be theminimum time period that the memory device 401 should wait prior toautomatically performing the background operations. The memory devicecan then acknowledge receipt and setting of this time period with anacknowledgement message 431.

FIG. 5 illustrates an execution phase of operation between the host 400and the memory device 401 as a result of the memory device 401supporting the host controlled enablement of automatic backgroundoperations. This phase of operation assumes that the host 400 hasdetermined that the memory device 401 supports the host controlledenablement of automatic background operations and that the memory devicehas been configured to enable this feature. For example, the method ofFIG. 4 might already have occurred.

The host 400 can transmit COMMAND1 (e.g., read or write command) 500 tothe memory device 401. The memory device 401 executes the receivedCOMMAND1 and transmits an acknowledgement 501 to the host 400 uponcompletion. For example, the memory device 401 can transmit a completionmessage to the host 400 when the commanded operation has been completed.

The host 400 might transmit another command, COMMAND2 (e.g., read orwrite) 510 to the memory device 401. The memory device 401 executes thereceived COMMAND2 and transmits an acknowledgement 511 to the host 400upon completion. For example, the memory device 401 can transmit acompletion message to the host 400 when the commanded operation has beencompleted.

There can then be a latency period 524 in the host 400 where the host400 is not transmitting commands to the memory device 401. Since thememory device 401 has already been instructed to not automaticallyperform background operations for a particular time period (e.g., timeperiod value), the memory device 401 is in an idle state 525 for thistime period. After the time period has expired, the memory device canautomatically perform 530 the background operations (e.g., housekeepingoperations). The automatic background operations are performed untilthey have been completed, the memory device loses power, or untilanother command is received from the host that interrupts the backgroundoperations. For example, the host 400 might transmit another commandCOMMAND3 520 to the memory device 401. Such a command would cause thememory device 401 to halt performance of the background operations inorder to service the interrupt.

In an alternate embodiment where a time register is not used, the host400 could transmit a start command to the memory device 401. The memorydevice 401 would remain in the idle state until receiving the startcommand. Upon receipt of the start command, the memory device 401 wouldstart background operations.

CONCLUSION

In summary, one or more embodiments of the method for host controlledenablement of automatic background operations in a memory device canprovide more reliable execution of the background operations since thehost is now aware of when the memory device is performing housekeepingtasks. Since the host enables the feature and informs the memory devicewhen it can automatically perform background operations, the host canknow the best time to interrupt the memory device with a command.Additionally, the host will know when not to shut off power for thememory device while the background operations are being performed.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations ofthe invention will be apparent to those of ordinary skill in the art.Accordingly, this application is intended to cover any adaptations orvariations of the invention.

What is claimed is:
 1. A method for host controlled enablement of anautomatic background operation in a memory device, the methodcomprising: determining at the host whether the memory device indicatesthat the memory device supports host controlled enablement of theautomatic background operation; and using the host to configure thememory device to perform the automatic background operation in thememory device in response, at least in part, to determining at the hostthat the memory device indicates that the memory device supports thehost controlled enablement of the automatic background operation.
 2. Themethod of claim 1 and further comprising writing a time period value toa register of the memory device.
 3. The method of claim 2 wherein thetime period is a time that the memory device should wait beforeautomatically performing the background operation.
 4. The method ofclaim 2 wherein the time period is a time that the memory device shouldwait before enabling the automatic background operation.
 5. The methodof claim 1 and further comprising transmitting a start command to thememory device configured to indicate to the memory device to start theautomatic background operation.
 6. The method of claim 1 whereindetermining at the host whether the memory device supports hostcontrolled enablement of the automatic background operation comprisesthe host reading a register of the memory device.
 7. The method of claim1 wherein using the host to configure the memory device to perform theautomatic background operation comprises the host transmitting controldata to the memory device.
 8. The method of claim 1 wherein using thehost to configure the memory device to perform the automatic backgroundoperation comprises the host writing control data to a register of thememory device.
 9. A method for host controlled enablement of anautomatic background operation in a memory device, the methodcomprising: determining if the memory device supports host controlledenablement of the automatic background operation; enabling the automaticbackground operation in the memory device based, at least in part, ondetermining that the memory device supports host controlled enablementof the automatic background operation; the host writing a time periodvalue to a first register of the memory device; and the host writing aunit of measure value for the time period value to a second register ofthe memory device.
 10. The method of claim 9 wherein the host writingcomprises the host directly writing to the first register withoutintervention of a controller of the memory device.
 11. The method ofclaim 9 wherein the host writing comprises the host writing to the firstregister with intervention of a controller of the memory device.
 12. Amethod for host controlled enablement of an automatic backgroundoperation in a memory device, the method comprising: determining if thememory device supports host controlled enablement of the automaticbackground operation; enabling the automatic background operation in thememory device based, at least in part, on determining that the memorydevice supports host controlled enablement of the automatic backgroundoperation; wherein determining if the memory device supports hostcontrolled enablement of the automatic background operation comprisesthe host reading a register of the memory device; and wherein the hostreading a first state from the register indicates that the memory devicesupports host controlled enablement of the automatic backgroundoperation and the host reading a second state from the registerindicates that the memory device does not support host controlledenablement of the automatic background operation.
 13. A systemcomprising: a host; and a memory device coupled to the host; wherein thehost is configured to determine whether the memory device indicates thatthe memory device supports host controlled enablement of an automaticbackground operation; and wherein the host is configured to configurethe memory device to perform the automatic background operation in thememory device in response, at least in part, to the host determiningthat the memory device indicates that the memory device supports thehost controlled enablement of the automatic background operation. 14.The system of claim 13 wherein the memory device further comprises aplurality of registers comprising a status register, an enablementregister, and a time register.
 15. The system of claim 14 wherein theplurality of registers further comprises a unit of measure registerassociated with the time register.
 16. The system of claim 14 whereinthe status register is a read only register and the enablement registerand time register are write/read registers.
 17. The system of claim 14wherein the status register is not programmable by the host.
 18. Thesystem of claim 14 wherein the host is configured to write control datato the enablement register wherein the control data is configured toenable or disable automatic performance of the automatic backgroundoperation by the memory device.
 19. The system of claim 14 wherein thehost is configured to write a time period value to the time registerwherein the time period value is indicative of when the memory devicecan automatically perform the automatic background operation.
 20. Thesystem of claim 14 wherein the host is configured to write a time periodvalue to the time register wherein the time period value is indicativeof a time when the memory device is enabled for the automatic backgroundoperation.
 21. The system of claim 13 and further comprising a registerhaving different register bits configured to selectively enabledifferent automatic background operations.